Ring armature telephone receiver



May 9, i950 E. E. MOTT RING ARMATURE TELEPHONE RECEIVER Filed June 18,1947- IIHIA I1 wk Num/j /Nl/E/vro@ E. E. MOT?" A TTORNEV Patented May 9,1950 UNITED STATES PATENT OFFICE to Beil Telephone Laboratories,Incorporated New York, N. Y., a corporation of New York Application June18, 1947, Serial No. 755,521

6 Claims.

This invention relates to electro-acoustic transducers and moreparticularly to ring armature type telephone receivers and transmitterssuch as disclosed in Patent 2,249,160, granted July 15, 1941, to EdwardE. Mott and application Serial No. 755,397, filed June 18, 1947, ofRobert E. Wirsching.

Ring armature devices of the type disclosed in the above-identiedapplication and patent comprise, in general, a magnetic circuitincluding a permanent magnet and an annular pole-piece, an annulararmature supported adjacent one margin and having its other margin injuxtaposition to the pole-piece, and a signal coil coupled to thecircuit to effect vibration of the armature in accordance with currentssupplied to the coil or, conversely, to establish signal currents inaccordance with vibrations of the armature.

The translating efciency of such device is dependent, of course, uponthe coupling between the coil and the signal flux path and, morespecifically, upon the reluctance of the path for this flux. In priordevices, the arrangement of the elements constituting the magneticsystem is such that the circuit for the signal ux includes, in additionto the armature and the pole-piece, at least a portion of the magnet.Generally, permanent magnet materials have relatively high reluctance sothat a circuit in which they are included has correspondingly highreluctance.

One object of this invention is to increase the efficiency oftranslation of electro-acoustic transducers.

More specifically, one object of this invention is to realize a lowreluctance path for the signal flux in ring armature type receivers andtransmitters.

In accordance with one feature of this invention, in a ring armaturetransducer of the general construction described above, the magneticsystem is constructed to effect maximum separation of the direct currentor polarizing and signal ilux paths.

More specifically, in accordance with one feature of this invention, themagnetic system includes an auxiliary or branch member separate from themagnet and dening with the polepiece and armature a low reluctance pathfor the signal ux.

In one specic and illustrative construction, the branch member,pole-piece and armature are associated to substantially enclose thesignal coil whereby good coupling between the coil and the signal uxpath is assured.

The invention and the above-noted and other features thereof will beunderstood more clearly and fully from the following detaileddescription with reference to the accompanying drawing in which:

Fig. 1 is a side View in section of an electroacoustic transducerillustrative of one embodiment of this invention;

Fig. 2 is a detail, diagrammatic view illustrating the flux paths in thetransducer shown in Fig. 1; and

Fig. 3 is a sectional view of a portion of an electro-acoustictransducer illustrative of another embodiment of this invention.

Referring now to the drawing, the device illustrated in Fig. 1, whichmay be used as either a receiver or transmitter, comprises a permanentmagnet having a cylindrical Iportion i9 and annular portion II,magnetized to produce poles at opposite extremities as indicated by theletters N and S. The cylindrical portion Ie is amxed, as by soldering,to the base I2 of an annular, L- sectioned pole-piece having acylindrical pole tip portion I3 coaxial with the magnet portion I 0.

Aiiixed to and extending from the base I2 is a cylindrical auxiliarymember Ed coaxial with the pole tip portion I3 and having its free endface accurately coplanar with the pole tip face oi the portion I3. Anannular` armature I5 overlies the faces noted, is coaxial therewith andis seated at its outer periphery upon an annular magnetic spacer I6 ofhigh permeability. The latter is of preassigned thickness and, thus,determines the normal spacing between the armature and the pole tipportion i3.

A non-magnetic member il', which may be of insulating material such as aphenolic condensation product, is interposed between the magnet andauxiliary member and has an annular lange I8 overlying the armature,this iange serving as a stop to prevent contact of the armature with themagnet portion II and sticking of the armature thereto. As shown in Fig.l., an inner surface portion of the member i? may engage the outerperipheral part of the armature, thereby to loosely hold the armature.Alternatively, inner surface of the member i? may be spaced slightlyfrom the armature so that the latter is loosely supported.

The armature mounts a dished, non-magnetic lightweight diaphragm I9,which may be of thin metal, such as Duralumin, or of thin plastic, suchas polystyrene.

A cylindrical signal coil 20 is mounted between the pole-piece portionI3 and the auxiliary member I4.

It will be noted that the signal coil is substantially enclosed by thepole-piece, armature and auxiliary member. The last three mentionedelements are made of high permeability material and, as will be pointedout in detail presently, define a low reluctance path for the signalflux closely linked to the signal coil. In one specific construction,these three elementsmay be constructed of the alloy, composed of 45 percent nickel and balance iron, known commercially as Permalloy.

The magnetic circuits oi the device are illustrated in Fig. 2, whereinthe paths followed by the direct current flux due to the magnet areindicated by the full arrows and the signal flux ow is indicated by thebroken arrows. Specifically, as indicated in this figure, the directcurrent iiux flowing from the north pole of the magnet divides, aportion thereof passing through the armature to the auxiliary membereid,thence to the base I2 of the pole-piece and to the south pole of themagnet, the remainder flowing across the gap between the armature andpolepiece portion I3 and thence through the pole-piece to the south poleof the magnet. The path for the signal flux, however, is separate fromthe magnet and is dened by the armature, the armature to pole-piece gap,the pole-piece portion I3, a part of the polepiece base I2, theauxiliary member Ill and the spacer 5. Inasmuch as the armature,pole-piece, auxiliary member and spacer I6 all are of high permeabilitymaterial, it will be appreciated that a very low reluctance for thesignal flux path or circuit obtains whereby a high force factor andoperating eiciency are realized.

It will be noted that the auxiliary member is spaced substantially fromthe permanent magnet so that out Very little short-circuiting of thepermanent magnet flux occurs. Y

In some cases, it may be desirable, for example because of restrictionsupon the diameter of the magnet and diaphragm that may be employed tomeet space or operating requirements, that the auxiliary member bepositioned in proximity to the cylindrical portion I of the permanentmagnet. An advantageous construction for such cases is illustrated inFig. 3. In this construction, the auxiliary member IAA is made of amaterial having a permeability higher than that of the magnet I0 and i Ibut lower than that of the polepiece to limit the short-circuiting ofthe direct current ilux. If the pole-piece is of Permalloy and themagnet is of an aluminum-nickel-cobalt-iron alloy known commercially asAlnico, the auxiliary member may be of Permalloy dust or of a mixture ofmagnetic and non-magnetic materials. The spacer IGA may be of magneticor non-magnetic material to provide a desired division of the directcurrent ilux between the armature and the pole-piece portion I3. Thesignal flux path includes the armature, pole-piece and auxiliary memberIdA, and, inasmuch as the latter is of permeability high in comparisonto that of the magnet, it will be appreciated that a relatively lowreluctance circuit for the signal flux is attained.

As in the embodiment illustrated in Fig. 2, in the construction shown inFig. 3, the free end of the auxiliary member is coplanar with the poleface of the pole-piece portion I3 and the normal armature to pole-piecegap is determined by the spacer IBA. Also, contact of the armature withthe magnet part II is prevented by the nonmagnetic member IBA.

It will be noted, additionally, that in both the embodiments illustratedthe normal air gap between armature and pole tip is realizedexpeditiously and involves no working of hard materials, such aspermanent magnet materials. The coplanar ends of the pole tip portion I3and auxiliary member I4 may be made accurately so by grinding, thesemembers being of readily workable materials.

Although specic embodiments of the invention have been shown anddescribed, it will be understood that they are but illustrative and thatvarious modifications may be made therein without departing from thescope and spirit of this invention'as dened in the appended claims.

What is claimed is:

l. An electro-acoustic transducer comprising a pole-piece having a baseand a pole tip, permanent magnet means having a first portion of onepolarity coupled to said base and a second portion of the oppositepolarity in juxtaposition to said pole tip and deiining an air gaptherewith, a magnetic support having one end magnetically coupled tosaid rst portion of said magnet means, and a vieratory member includinga magtic armature, said armature being mounted Vby tn e other end ofsaid support and extending into said air gap, said other end of saidsupport being coupled magnetically to said second portion of said magnetmeans only by way of said armature.

2. An electro-acoustic transducer comprising a pole-piece having anannular base and a cylindrical pole tip portion extending from saidbase, said base extending outwardly from one end of said pole tipportion, a cylindrical magnetic support extending from said base andspaced from and coaxially encompassing said pole tip portion, a signalcoil in electromagnetic coupling relation with said. pole piece andsupport, an annular armature coaxial with said pole tip portion andhaving its inner marginal portion adjacent the pole tip thereof, saidarmature being mounted adjacent its outer margin by said support, Vandpermanent magnet means having one pole magnetically coupled to said baseand its other pole opposite said pole tip and defining an air gaptherewith, said other pole being magnetically coupled to said supportonly through said armature.

3. An electro-acoustic transducer comprising a cylindrical pole-piecemember, a cylindrical mag--V netic member coaxially encompassing saidpole piece member and spaced therefrom, a permanent magnet having acylindrical part coaxially encompassing said magnetic member and havinga flange extending from one end of said cylindrical part intojuxtaposition to one end of said pole-piece and defining an air gaptherewith, the inner marginal portion of said flange and the other endof said cylindrical part Vbeing of opposite polarity, means magneticallycoupling said other end of said cylindrical part, the other end of saidpole-piece member and the corresponding end of said magnetic membertogether, a signal coil between said pole-piece and magnetic member, andan annular armature having its inner marginal portion free and in saidair gap and having an outer portion in juxtaposition to the other end ofsaid magnetic member, said other end of said magnetic member beingcoupled magnetically to said inner marginal portion of said flange onlythrough said armature.

4. An electro-acoustic transducer in accordance with claim 3 whereinsaid magnetic member is spaced from said cylindrical magnet part andsaid magnetic member and pole-piece member are of high permeabilitymaterial.

5. An electro-acoustic transducer in accordance With claim 3 whereinsaid magnetic memloei` is immediately adjacent to said cylindricalmagnet part and is of lower` permeability than said pcle-piece member.

6. An electro-acoustic transducer comprising an annular magneticarmature, means defining a low reluctance signal ux magnetic circuitincluding said armature and a pole piece having a loa-se and acylindrical portion extending from said base, coaxial With said armatureand termihating in a pole tip in juxtaposition to one face of saidarmature at the inner margin thereof, said means including also acylindrical magnetic support encompassing and spaced from saidcylindrical portion and having one end seated upon said hase, saidarmature being supported adjacent its periphery from the other end ofsaid support, a signa-l coil coupled to said circuit, and

d means for producing a polarizing flux threading said armature radiallycomprising a permanent magnet having one pole coupled to said base andits other pole in juxtaposition to the other face of said armature atsaid inner margin thereof.

EDWARD E. MOTT.

REFERENCES CITED The following references are record in the ille of thispatent:

UNITED STATES PATENTS Number Name Date 1,579,695 Gavin Api'. 6, 19261,721,217 Hineline July 16, 1929 1,895,071 Fanger Jan. 24, 19331,986,856 Ringel Jan. 8, 1935 2,170,571 Mott Aug. 22, 1939 2,249,160Mott July 15, 1941

